Saturday, May 31, 2014

Rice paddies, China,
circa 1917-1923 (source). To grow rice, you must cooperate with neighbors for
irrigation and labor. Today, even with the shift to a post-agricultural
society, Chinese from rice-farming areas display less individualism and more interdependence
than Chinese from wheat-farming areas. Is this evidence of gene-culture
co-evolution?

Human populations differ
in genetic variants that influence a wide range of mental and behavioral
traits. These differences are statistical, often being apparent only when one
compares large numbers of individuals. Yet even a weak statistical difference
can affect the way a culture develops. Furthermore, the way a culture develops
may favor certain genetic variants over others.

East Asian
cultures, for example, have diverged noticeably from European cultures,
particularly those of Western Europe:

Western culture is
more individualistic and analytic-thinking, whereas East Asian culture is more
interdependent and holistic-thinking. Analytic thought uses abstract categories
and formal reasoning, such as logical laws of noncontradiction—if A is true,
then "not A" is false. Holistic thought is more intuitive and
sometimes even embraces contradiction—both A and "not A" can be true.
(Talhelm et al., 2014)

This is of course a
generalization that ignores differences within each culture area. Historically,
abstract thinking has been stronger among the French, whereas the English have tended
toward empirical "bottom-up" thinking. A new study suggests that
similar differences exist within East Asia, specifically between rice-farming
areas and wheat-farming areas. In short, rice farming favors interdependence,
whereas wheat farming is more conducive to individualism:

The two biggest
differences between farming rice and wheat are irrigation and labor. Because
rice paddies need standing water, people in rice regions build elaborate
irrigation systems that require farmers to cooperate. In irrigation networks,
one family's water use can affect their neighbors, so rice farmers have to
coordinate their water use. Irrigation networks also require many hours each year
to build, dredge, and drain—a burden that often falls on villages, not isolated
individuals. (Talhelm et al., 2014)

Labor inputs are
thus greater for rice growing. A husband and wife cannot farm a large enough
rice paddy to support their family if they rely only on their own labor. This
is not the case with wheat farming:

In comparison,
wheat is easier to grow. Wheat does not need to be irrigated, so wheat farmers
can rely on rainfall, which they do not coordinate with their neighbors.
Planting and harvesting wheat certainly takes work, but only half as much as
rice. The lighter burden means farmers can look after their own plots without
relying as much on their neighbors. (Talhelm et al., 2014)

A study of 1,162
Han Chinese found differences between rice-farming and wheat-farming regions on
three psychological measures: cultural thought, implicit individualism, and
loyalty/nepotism.

Cultural thought

The triad task
shows participants lists of three items, such as train, bus, and tracks.
Participants decide which two items should be paired together. Two of the items
can be paired because they belong to the same abstract category (train and bus
belong to the category vehicles), and two because they share a functional
relationship (trains run on tracks). People from Western and individualistic
cultures choose more abstract (analytic) pairings, whereas East Asians and
people from other collectivistic cultures choose more relational (holistic)
pairings.

[...] People from
provinces with a higher percentage of farmland devoted to rice paddies thought
more holistically. [...] Northern and southern China also differ in several
factors other than rice, such as climate, dialect, and contact with herding
cultures. Therefore, we analyzed differences among neighboring counties in the
five central provinces along the rice-wheat border. [...] People from the rice
side of the border thought more holistically than people from the wheat side of
the border. (Talhelm et al., 2014)

Implicit
individualism

Researchers measure
how large participants draw the self versus how large they draw their friends
to get an implicit measure of individualism (or self-inflation). A prior study
found that Americans draw themselves about 6 mm bigger than they draw others,
Europeans draw themselves 3.5 mm bigger, and Japanese draw themselves slightly
smaller.

People from rice
provinces were more likely than people from wheat provinces to draw themselves
smaller than they drew their friends. [...] On average, people from wheat
provinces self-inflated 1.5 mm (closer to Europeans), and people from rice
provinces self-inflated -0.03 mm (similar to Japanese). (Talhelm et al., 2014)

Loyalty/nepotism

One defining
feature of collectivistic cultures is that they draw a sharp distinction
between friends and strangers. A previous study measured this by having people
imagine going into a business deal with (i) an honest friend, (ii) a dishonest
friend, (iii) an honest stranger, and (iv) a dishonest stranger. In the
stories, the friend or stranger's lies cause the participant to lose money in a
business deal, and the honesty causes the participant to make more money. In
each case, the participants have a chance to use their own money to reward or
punish the other person.

The original study
found that Singaporeans rewarded their friends much more than they punished
them, which could be seen positively as loyalty or negatively as nepotism.
Americans were much more likely than Singaporeans to punish their friends for
bad behavior.

[...] People from
rice provinces were more likely to show loyalty/nepotism [...]. In their
treatment of strangers, people from rice and wheat provinces did not differ.
(Talhelm et al., 2014)

Gene-culture
co-evolution?

Interestingly,
these findings come from people who have no connection to farming of either
sort. If these psychological traits have survived the transition to a
post-agricultural and largely urban society, how are they passed on? The
question is raised by the authors:

[…] perhaps the
parts of culture and thought style we measured are more resistant to change. Or
perhaps modernization simply takes more generations to change cultural
interdependence and thought style. However, most of our participants were born
after China's reform and opening, which started in 1978. Furthermore, Japan,
South Korea, and Hong Kong modernized much earlier than China, but they still
score less individualistic on international studies of culture than their
wealth would predict. (Talhelm et al., 2014)

The authors do not
use the term "gene-culture co-evolution" but this seems to be the
explanation they implicitly favor. Over many generations, rice farming has
selected for a certain package of psychological traits, i.e., less abstract
thinking and more functional "holistic" thinking; less individualism
and more collectivism; and less impartiality toward strangers and more
favoritism towards kin and friends.

The predominance of
rice farming in East Asia may thus explain why East Asian cultures have
developed their pattern of psychological traits:

The rice theory can
explain wealthy East Asia's strangely persistent interdependence. China has a
rice-wheat split, but Japan and South Korea are complete rice cultures. Most of
China's wheat provinces devote less than 20% of farmland to rice paddies. None
of Japan's 9 regions or South Korea's 16 regions has that little rice (except
for two outlying islands). Japan and Korea's rice legacies could explain why
they are still much less individualistic than similarly wealthy countries.
(Talhelm et al., 2014)

Saturday, May 24, 2014

Taylor Swift (photo by David Shankbone). The physical appearance of
Europeans seems to result from a selection pressure that acted primarily on
women and only secondarily on men. This is especially true for highly visible traits
on or near the face—the focus of visual attention.

I have just published a paper on "The puzzle of
European hair, eye, and skin color." The introduction is reproduced below
(reference citations have been removed for ease of reading). The full text is
available here.

****************************************************

Most humans have black hair, brown eyes, and brown
skin. Europeans have a different color scheme, their hair being also brown,
flaxen, golden, or red, and their eyes also blue, gray, hazel, or green.
Finally, their skin is pale, almost like an albino's.

How did this unusual color scheme come about? Perhaps
the genetic change that lightened the skin also affected the hair and the eyes.
Yet the genes are different in each case. European skin lightened mainly
through the appearance of new alleles at three genes: SLC45A2, SLC24A5,
and TYRP1. European hair color diversified through a proliferation of
new alleles at MC1R. European eye color diversified through a
proliferation of new alleles in the HERC2-OCA2 region and elsewhere.

Light skin is associated with a few of the new hair
and eye color alleles, particularly the ones for red hair or blue eyes.
Conceivably, these alleles may be a side effect of selection for lighter skin.
But why would such selection increase the total number of alleles for hair and
eye color, especially when so many of them have little or no effect on skin
color? And why have neither red hair nor blue eyes reached fixation in any
human population, even those with milk-white complexions?

The European color scheme has another puzzling aspect.
It seems to result from a selection pressure that acted primarily on women and
only secondarily on men:

- Hair color varies more in women than in men.
Redheads are especially more frequent among women.

- Eye color varies more in women than in men when both
copies of the so-called blue-eye allele are present, the result being a greater
diversity of female eye colors wherever blue eyes are the single most common
phenotype, i.e., in northern and eastern Europe.

- Blue eyes are associated in men with a more feminine
face shape.

- In all human populations, women are paler than men
after puberty. This post-pubescent lightening is due to sexual maturation and
not to differences in sun exposure. In women, lightness of skin correlates with
thickness of subcutaneous fat and with 2nd to 4th digit ratio—a marker of
prenatal estrogenization. Admittedly, this sex difference is not greater in
Europeans than in other populations, although it could not easily be otherwise,
since Europeans are so close to the physiological limit of depigmentation.

While women are more diverse than men both in hair and
eye color, this greater diversity came about differently in each case. With
hair color, women have more of the intermediate hues because the darkest hue
(black) is less easily expressed. With eye color, women have more of the
intermediate hues because the lightest hue (blue) is less easily expressed.

In sum, European hair and eye color diversified
through a selection pressure that acted on different genes via different
pigmentary changes. The common denominator seems to be the creation of new visual
stimuli on or near the face—the focus of visual attention.

Saturday, May 17, 2014

Robert Chambers
(1802-1871). His anonymously published book, Vestiges of the Natural History of Creation (1844), helped pave
the way for public acceptance of Darwin’s theory of evolution. (source)

I haven't yet read
Nicholas Wade's book A Troublesome Inheritance. I will venture to say,
however, that it will be remembered less for its actual content than for its
role in encouraging discussion of a difficult topic. In particular, it will
familiarize a broad audience with the following points:

1. Biological
evolution did not slow down with the advent of cultural evolution. In fact, it
speeded up, particularly when farming began to replace hunting and gathering
some 10,000 years ago. At that time, the pace of genetic change may have risen
a hundred-fold.

2. Cultural
evolution diversified the range of human environments. Instead of adapting only
to differences in climate or food sources, like other animals, our species also
adapted to differences in social structure, in the division of labor, in the
means of subsistence, in unwritten or codified norms of conduct, in the degree
of sedentary living, and in many other human-made phenomena. Our ancestors
reshaped their environments, and these human-made environments reshaped them
via gene-culture co-evolution.

3. This
gene-culture co-evolution persisted into modern times. The English population,
for instance, evolved between the twelfth and nineteenth centuries in terms of
certain behavioral traits, particularly future time orientation and distaste
for violence as a means to settle personal disputes. As Gregory Clark has
shown, this behavioral change resulted from a demographic change—the relative
reproductive success of the middle and upper classes—which altered the
composition of the English gene pool. So the mantra that "we, too, were
once savages" does not, in fact, deny the reality of biological evolution.
It affirms it.

4. Human
populations thus differ not only anatomically but also in various mental and
behavioral predispositions. These differences are statistical and often
apparent only when one compares large numbers of people. But even a weak
statistical difference can profoundly affect how a society will develop and
organize itself.

5. Finally, Richard
Lewontin was right when he reported that genes vary much more within
populations than between populations. He was unaware, however, that genetic
variability between populations is qualitatively different from genetic
variability within a population. The more a gene has value, the more it will
vary across a population boundary, since such boundaries usually coincide with
barriers that separate different habitats, different environments, different
means of subsistence and, hence, different selection pressures. Conversely, the
less a gene has value, the more it will vary within a population, that is,
among individuals who share similar conditions of life. The selection pressure
is uniform but this uniformity will not level out the variability of such genes
within the population—much as a steam iron will smooth a rumpled shirt—since
this variability is less phenotypically significant, i.e., it produces fewer
functional differences that natural selection can act on.

Are there
questionable points in Wade's book? Undoubtedly. But we should not wait until
all issues are settled before we put pen to paper. Writing is a process where
ideas are shared with a broader audience for debate. We may forget that The
Origin of Species was written without any knowledge of Mendelian genetics.
We may also forget, or simply not know, that Darwin’s path to public acceptance
was cleared by an earlier book: Vestiges of the Natural History of Creation
(1844). Although its anonymous author, Robert Chambers, had no understanding of
natural selection, he nonetheless played a key role in familiarizing the public
with the fossil record and the reality of biological change over time. As one
historian pointed out:

It is customary
among biographers of Darwin to speak of the excitement which greeted the
appearance of the Origin and of Huxley's able defense of Darwin at
Oxford in his clash with Bishop Wilberforce. Actually, however, by the time
Darwin published, Robert Chambers had drawn much of the first wrath of the
critics and the intelligent public was at least reasonably prepared to consider
a more able, scientific presentation of the subject.

[…] The attacks
which the scientific world launched upon the Vestiges have, in
retrospect, a quite unreal character. They belabor minutiae and amateurish
minor errors as though there was some subconscious recognition that the heart
of the thesis was unassailable.

[…] With its
publication and success as a best seller, the world of fashion discovered
evolution. The restricted professional worlds of science and of theology both
lost their ability to suppress or intimidate public thinking upon the matter.

[…] By 1859, when
the Origin of Species was published, an aroused and eager audience was
considerably prepared for the revelations of Charles Darwin. The great amateur
disputant and the great professional scholar should always be remembered as
having together won the public mind to evolution. (Eiseley, 1958, pp. 134, 138,
139)

References

Chambers, R.
(1844). Vestiges of the Natural History
of Creation, London: John Churchill

Saturday, May 10, 2014

The digit ratio is the length of the index finger (2nd
finger) divided by the ring finger (4th finger). It correlates with
the degree of androgenization or estrogenization of fetal tissues, including
the fetal brain. (source)

As small bands of hunter-gatherers gave way to larger
and more complex societies of farmers and townsfolk, trusting relationships had
to expand beyond the circle of close kin. This larger social environment posed
a two-fold problem:

For trust to evolve our ancestors must have 1) overcome
the incentive to defect when involved in cooperative activity, and 2)
suppressed the proclivity to use violence to take resources from conspecifics,
as is seen in nonhuman primates. (Gifford, 2013)

This in turn required "social rules of governance
and implicit institutions that suppressed free riding, provided rules of
orderly behavior that increased cooperation by making individual behavior
predictable, and also protected the property rights of individuals"
(Gifford, 2013).

But what, exactly, does one do with free riders and
sociopaths? Traditionally, such people were excluded from society, either by
ostracism or, in more serious cases, by execution. There was thus strong
selection for pro-social behavior, i.e., acting honorably and peacefully with other
members of society. This selection operated even when ostracism was far from
permanent or total. Shunning, public shaming, or simply a bad reputation would
hurt one's chances for survival and reproduction in many ways: reduced access
to community goods, discrimination on the marriage market, reluctance by others
to provide assistance, and so forth.

This process of selection had genetic consequences,
since nearly all behavioral traits have a heritability of 40% plus or minus
20%. There was thus removal not only of antisocial individuals from society but
also of antisocial predispositions from the gene pool. The corollary was that
the gene pool became dominated by pro-social predispositions, particularly
empathy, compliance with social rules, and high thresholds for expression of
anger.

This evolution probably occurred incrementally through
small changes at many genes. This is what we see with increases in human
intellectual capacity, and it is probably a general rule for the evolution of
complex traits. Big changes at single genes tend to have nasty side-effects
elsewhere on the genome.

A recent paper has highlighted one possible
evolutionary pathway: the relative degree of androgenization or estrogenization
of the developing fetus (Branas-Garza et al., 2013). By varying the ratio of
one to the other, it's possible to alter a wide range of behavioral tendencies.
This prenatal priming of fetal tissues can be easily measured by the
"digit ratio," i.e., the length of the index finger (2nd finger)
divided by the length of the ring finger (4th finger). The lower your digit
ratio, the more you have been androgenized before birth. The higher your digit
ratio, the more you have been estrogenized before birth.

We analyze the association between altruism in adults
and the exposure to prenatal sex hormones, using the second-to-fourth digit
ratio. We find an inverted U-shaped relation for left and right hands, which is
very consistent for men and less systematic for women. Subjects with both high
and low digit ratios give less than individuals with intermediate digit ratios.
We repeat the exercise with the same subjects seven months later and find a similar
association, even though subjects' behavior differs the second time they play
the game.

Different environments favor different degrees of
altruism. In one setting, an altruist may be admired and enjoy preferential
access to community goods. In another, the same person may be ridiculed and
ruthlessly exploited. Thus, according to the context, the right balance has to
be struck between altruism and selfishness:

One possible interpretation of the above findings
comes from stabilizing selection. Since sharing with others is socially
beneficial, selfish individuals are socially excluded and their fitness
affected negatively. If individuals who are exposed too much or too little do
not share with others, there is an evolutionary pressure on these non-altruistic
individuals, which in turn generates an indirect evolutionary pressures on the
degree of exposure to prenatal sex hormones by raising survival probabilities
of individuals with intermediate levels of exposure. This hypothesis is
supported by observed distributions of 2D:4D in the literature, which are
universally concentrated around the median values. (Branas-Garza et al., 2013)

From one population to the next, digit ratios tend to
cluster around different means, perhaps because altruism has been favored or
disfavored to different degrees. This social selection may have targeted other
behavioral traits, notably thrill-seeking. Kornhuber et al. (2013) have found
that low digit ratios are associated with video game addition. This kind of
addiction may tap into a male need for risk and adventure, which may likewise have
been more adaptive in some environments than in others.

Saturday, May 3, 2014

A steady increase in reaction time seems to begin
circa 1980 in Sweden, Great Britain, and the United States (h/t to hbd* chick)

Has reaction time been steadily increasing from
generation to generation? This was the finding of a paper last year, which
argued that mean IQ had fallen in Britain by 13 points since Victorian times
(Woodley et al., 2013). The problem here was not the extrapolation from
reaction time to IQ, which in any case should not have changed over the past
century. The problem was the possibility of sampling bias. The early samples
(from the Victorian age) were slanted toward people of elite origin. In one
case, they were University of Chicago students; in the other, museum visitors
who had paid to take the reaction test. In contrast, the recent samples were
much more representative, largely because the educational system had become
more universal. Thus, the drop in reaction time over time may be largely, if
not wholly, an artefact of better sampling of the general population (hbd* chick, 2013).

This criticism seems less applicable to a study of
this drop in more recent times. This study was presented as a conference paper
and only the abstract is available. But it does seem interesting:

Here, we show that change in genetic intelligence
can be estimated, independently of the Flynn effect, by way of simple reaction
time (RT). Data from three studies with different samples from Sweden, UK, and
USA converge at an RT increase of 0.7-0.9 ms per year, which corresponds to a
decrease in intelligence of between 4 and 5 IQ points per generation, or
1.3-1.7 points per decade in these countries. (Madison, 2014)

That’s a big jump in reaction time. Moreover, most
of the increase seems to be squeezed into the last six years of the study, from
1980 to 1985 (see above chart). No selection pressure could have produced such
a change over such a short time. So what could possibly be going on here?

Keep in mind that Sweden, the United Kingdom, and
the United States are not closed systems. All three countries are open to the
world, and the early 1980s corresponded to a time when they became much more
open. Consequently, we are not looking at change within a population, but
rather the replacement of one population by another, and this change would have
been most noticeable in the school classrooms where these tests were conducted.

The other finding of this study is that the Flynn
Effect has been masking a decline in intellectual capacity. Yes, we’re getting
better at giving standardized answers to standardized questions, but this
change doesn’t reflect an actual increase in intelligence. We’re just
allocating more and more mental resources to the task of test-taking. The
reaction time data suggest that real intellectual capacity has been declining
since circa 1980.

At the same conference, Armstrong (2014) likewise
argues that the Flynn Effect may be illusory for the most part:

However, "general intelligence", the
biological substrata which cause the positive manifold amongst different IQ
tests, has not increased, since the sizes of Flynn effects on different tests
are inversely related to those tests' g loadings. The same pattern holds
amongst items. Thus, for example, vocabulary size (generally the most or among
the most g loaded tests) has shown a small Flynn effect, and by some measures even
a decline. However, the "Coding" test (from the Wechsler) or the
"Draw-a-Man" test both have low g loadings and have shown very large
Flynn effects.

To date, Madison’s paper is unavailable. All we have
is an abstract that raises more questions than it answers. We will have to wait
for the full paper before a thorough assessment can be made.

Woodley, M.A., J. Nijenhuis, and R. Murphy. (2013).
Were the Victorians cleverer than us? The decline in general intelligence estimated
from a meta-analysis of the slowing of simple reaction time, Intelligence, 41, 843-850.

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Welcome to my blog! For the most part, this page will be an extension of my website, with comments relating to my research. But it will also branch out into more general discussions of human evolution.